1. Field of the Invention
The present invention relates generally to navigation control systems for aircraft. More specifically the present invention relates to a vertical flight planning and management system for use with aircraft.
2. Background of the Invention
The performance prediction function in a flight management system (FMS) uses equations of motion, aerodynamic and engine characteristics to simulate an intended flight plan. Using available data, the flight trajectory is computed from origin through destination. This flight plan must not, for example, violate any speed or altitude constraints or other such restrictions imposed by the Federal Aviation Administration (FAA), airline policies, or pilot entries. In well-known FMSs, computed waypoint arrival times and fuel status may be displayed to the pilot as an aid in evaluating various route options, monitoring progress, contingency planning, etc.
An FMS performs the task of flight planning by compiling a four-dimensional route, defined by a lateral flight plan (i.e., two of the four dimensions), a vertical flight plan and an elapsed time trajectory. These flight plans are compiled from stored navigation databases and flight-crew entries. The FMS performs the task of navigation by identifying aircraft position relative to fixed points on the surface of the earth. A lateral position, vertical position and elapsed time are computed by a combination of data from ground-based transponder radios, Global Positioning System, and aircraft motion sensors. The FMS performs the task of guidance by determining the appropriate altitude, speed, thrust, and heading required to fly the current leg of the flight plan. These targets are determined by a comparison of aircraft position (navigation) to the desired profile (flight planning) and may take into account temporary deviations from the flight plan due to weather, traffic, equipment failure or on-board emergencies. The autopilot controls pitch, roll, and yaw control surfaces and the throttle position, to instantaneously maintain the desired aircraft trajectory defined by FMS guidance.
Currently, with a traditional FMS, the vertical flight plan follows a fixed sequence of flight phases including: takeoff, climb, cruise (which may include one or more step climbs), descent (which may include options for early or late descent), and approach (which may include an optional “go around” for a missed approach). These discrete phases are shown in FIG. 1. A pilot usually enters specific vertical flight plan parameters associated with this fixed sequence, such as climb, cruise, and descent airspeeds, and cruise altitude.
FIG. 2 depicts the classic method of performing calculations for an existing vertical trajectory model in an existing FMS. As can be readily appreciated, this series of calculations is tied to the notion of a fixed sequence of flight phases. The performance calculations review each of the various phases of the vertical flight plan (VFP) and check to ensure that flight is within the preset parameters. Calculations predict flight time and fuel consumption according to the flight plan. One problem with this structure is that any change or addition to the general structure of the vertical flight plan (e.g., multiple climb-cruise-descent phases) requires that all of the performance prediction logic be pulled apart and modified. Changes to the FMS in this manner have proven to be very time consuming and expensive. In addition, the resulting performance prediction function remains limited in the types of trajectories it is capable of supporting.
Thus, within a given flight phase, the possible trajectories that can be described are very constrained. For example, in cruise, a pilot must fly a fixed altitude segment. Although some systems allow for step climb capabilities, there are no trajectory parameters that can be entered by the pilot that would allow the user to fly, for example, a “cruise-climb” segment. As used herein, cruise-climb refers to continuously climbing as fuel is burned to achieve optimum efficiency. In the air traffic control (ATC) environment of the past, this was not as important because FAA controllers assigned aircraft to fly to a fixed altitude. However, in the evolving ATC environment, aircraft may receive block altitude clearances such that a cruise-climb segment could be part of a legal and approved vertical flight plan.
Also, as more user-preferred options become available, the vertical flight plans modeled within an FMS need to keep pace. Due to their current configuration, modifying the vertical flight plan alone within a comprehensive FMS is quite cumbersome and such modifications would be very difficult. The changes would affect several functional areas of the FMS resulting in high costs of development and re-certification.